Aerospace blind fasteners are widely used in aircraft manufacturing. There are many different types and sizes that are used, based on the material or strength characteristics required. These blind fasteners are typically comprised of a sleeve, a stem and some type of locking mechanism. The stem of a fastener is gripped by jaws inside of a pulling head, while the sleeve of the fastener is biased against the front of the pulling head housing. The fasteners are installed by placing them in a hole prepared in the aircraft structure and pulling on a protruding stem accessible on the non-blind side.
The stem typically features a series of annular grooves, called serrations, which are to be engaged by the jaws of the pulling head used to install them. During installation, the stem is pulled away from the structure. While applying this pulling load to the stem, some type of deformation occurs on the blind side of the structure or inside of the hole, depending on the particular type of fastener used. Toward the end of the fastener installation cycle, a locking ring is deformed in place which locks the fastener in an installed position and the stem separates from the fastener.
The pulling heads generally used to install blind fasteners are comprised of a draw-bolt containing a set of jaws, and a housing that sets the locking mechanism and provides support to the fastener during installation.
In aerospace blind fastening systems, the gripping force provided by the jaws is very important for proper fastener installation—too little force causes slippage leading to installation failures and too much force makes it difficult to use the tool, which also causes productivity and tool wear issues. Straight pulling heads can easily be adjusted for the amount of grip the jaws provide, however offset or 90 degree pulling heads presently on the market do not provide adjustments for the grip of the jaws. For instance, the Cherry Aerospace Single Jaw Offset Pulling Head H781-456 is a popular tool with the aircraft manufacturers because of its low profile and its ability to reach into very tight areas. This tool, however, does not have a jaw grip adjustment so it sometimes has problems installing smaller diameter fasteners.
In order to address this issue, complicated set-up processes have been devised to try and address the slippage issue. However, despite the foregoing, the underlying problem coming from lack of proper adjustment still exists.
The present invention overcomes problems presented in the prior art and provides additional advantages over the prior art. More particularly, the present invention has been developed to address stem slippage issues inherent to the offset and 90 degree pulling heads, which has limited their usage. Such advantages will become clear upon a reading of the attached specification in combination with a study of the drawings.